The present invention relates to thermoplastic elastomers (TPE) and thermoplastic vulcanizates (TPV), also known in the art as dynamically vulcanized alloys (DVA), with improved gas-barrier properties.
Thermoplastic elastomer compositions useful as a gas-barrier layer in pneumatic tires are well known. For example, EP722850B1 discloses a low-permeability thermoplastic elastomer composition which comprises a low-permeability rubber, such as brominated poly(isobutylene-co-paramethylstyrene), referred to hereinafter as BIMS, dispersed in a low-permeability thermoplastic matrix, such as polyamide or a blend of polyamides.
Thermoplastic vulcanizates having improved coring properties are known from, for example, U.S. Pat. No. 6,946,522, which discloses a blend of thermoplastic polypropylene resin, vulcanized butyl rubber, a hydrogenated poly(styrene-b-isoprene-b-styrene) block copolymer and a polybutene oil plasticizer.
Thermoplastic vulcanizates having improved barrier properties are known from, for example, U.S. Pat. No. 7,060,753, which discloses a composition of high melt flow index thermoplastic olefin resin, butyl rubber and an oligomers of isobutylene and butene.
It is known that ethylene-vinyl alcohol copolymers (EVOH) have an excellent gas barrier property. Certain compositions exhibiting low gas permeability performance composed of thermoplastic resin-based blends such as a polyethylene terephthalate and vinyl alcohol-ethylene copolymer (PET/EVOH), where one thermoplastic resin is layered over the other layer to form plural layers by molding, are disclosed in Japanese Patent Application No. 7-55929. However, since these materials are thermoplastic resin/thermoplastic resin blends, while they are superior in gas barrier performance, they lack flexibility, and therefore, such films are subject to failure if they are used in a vehicle tire which is subject to significant stress and flexing.
A low permeability rubber laminate containing an EVOH layer bonded to a diene-based rubber layer comprising a silane-based coupling agent is disclosed in US 2008/0314490. The EVOH layer must be sufficiently thick to impart gas barrier properties, but sufficiently thin to avoid poor stretch flex fatigue.
There are continuing needs to improve the barrier properties of thermoplastic elastomers and dynamically vulcanized thermoplastic barrier films, and/or to improve the mechanical properties of films employing EVOH in a barrier layer.